input node random expression not used
In the second comment to my answer to the question you refer to, I mentioned having to update dependencies for the driver. This seems to be a manual step we need to perform when adding drivers to nodes.

You can find the driver details in the graph editor in driver display mode. With the driven value selected you need to click the Update Dependencies button and you should then find the node value will be updated properly.



Also ensure that you have enabled auto-run python scripts.

While work is being done on the new dependency graph it may be a good time to report this as a bug so that the developers can look into improving this.